NF-κB is reportedly a major regulator of ROS generation in leukemia cell lines [6] . However, the inhibitory mechanism of interleukin-6 (IL-6) in ROS generation remains unknown.

It is difficult to measure and monitor ROS in vivo because these substances are rapidly metabolized. A simple test for d-reactive oxygen metabolites (d-ROM) has been developed and is able to detect the total amount of ROS in the body [7] . Previous reports demonstrated that d-ROM values in RA patients were significantly higher than those in osteoarthritis patients [8] , and that d-ROM levels are significantly correlated with disease activity in RA [9] .

Then, the effect of tocilizumab (TCZ), an anti-IL-6 receptor antibody on d- ROM value in patients with RA was examined. The results in the current study demonstrated that TCZ significantly and rapidly downregulates ROS in serum of RA patients, with associated improvement of disease activity.

2. Materials and Methods2.1. Patients and Blood Samples

Eleven RA patients were recruited to this study. Patients with comorbidities such as diabetes mellitus, chronic kidney diseases more than grade 3, and chronic obstructive pulmonary disease (COPD) were excluded. RA patients who met the 1987 American College of Rheumatology diagnostic criteria [10] were recruited.

TCZ was administered to all patients according to the guidelines of the Japan College of Rheumatology, and was continued for at least 1 year. Detailed data are shown in Table 1. The average age was 54 ± 17 years (range 16 - 70; 4 males and 7 females). Steinbrocker Stage was II, III, and IV in 1, 5, and 5 cases, respectively. Steinbrocker Class was 2, 3, and 4 in 5, 4, and 2 cases, respectively. RA disease duration was 12 ± 13 years on average (0.2 - 37). There were 8 biologic-naive cases. Biologics had been used in 3 cases prior to TCZ, and included etanercept, infliximab and adalimumab, and adalimumab, respectively. Methotrexate had been used in 6 cases at an average dose of 4.2 ± 4.0 mg/week (0 - 8 mg/week). Methylprednisolone had been used in 7 cases at an average dose of 3.4 ± 3.0 mg/day (0 - 7 mg/day). The patients were registered from September 2009 to July 2012 and the study period to collect each data was determined to 12 months.

This observational study began after approval by the Institutional Review Board at Niigata University School of Medicine (ID number 1345) and had obtained ethical clearance. Informed consent was achieved for all the registered

patients. Blood sampling was performed on day 0 (immediately before initial TCZ treatment), and 3, 6, and 12 months later. Erythrocyte sedimentation rate (ESR) and serum matrix metalloproteinase-3 (MMP-3) levels were measured at each time point. Disease Activity Score (DAS28-4-ESR) was determined by tender and swollen joint counts and the visual analogue scale (VAS) on visits to the outpatient clinic.

2.2. Measurement of Oxidative Stress Markers in Serum

Venous blood samples were collected at each time point and serum oxidative stress markers were measured.

A Free Radical Elective Evaluator (FREE) (Diacron, Italy) was used according to the manufacturer’s protocol. A 20-μl serum sample was added to 1 ml of buffered solution (R2 reagent kit), and 20 μl of chromogenic substrate (R1 reagent kit) was added to the cuvette. After mixing, the sample was immediately incubated in the thermostatic block of the analyzer for 5 min at 37˚C. Absorbance was recorded at 505 nm. The measurement was recorded as Carratelli units (U.CARR; 1 U.CARR corresponds to 0.08 mg/dl H2O2). Reference values suggested by the manufacturer are <300 U.CARR. Values were defined for d-ROM; more than 300 U.CARR suggests high oxidative stress.

2.3. Statistical Analysis

All statistical analysis was performed using SPSS (Ver. 21) software (IBM, Chicago, IL, USA). P-values less than 0.05 were considered significant.

Paired t-tests were performed for each parameter (DAS28, d-ROM, MMP-3).

In our previous study, serum ROM values were high (525 U.CARR on average, at baseline), and decreased to 366 U.CARR on average in the final observation period with use of biologics in patients with RA. Simultaneously, DAS28-3-CRP, C-reactive protein (CRP), ESR, and MMP-3 were also decreased. However, in refractory RA cases, d-ROM values were never downregulated [13] .

In addition, we also previously reported that etanercept (ETN) prospectively reduced d-ROM values from 393 U.CARR at initiation to 337 U.CARR at 12 months after etanercept treatment. DAS28 score also improved from 4.69 at initiation to 2.60 at 12 months after etanercept treatment [14] . This result was in accordance with that in a previous report [4] . In the current study, we examined whether TCZ decreased serum levels of oxidative stress markers in association with DAS28 improvement in a time-dependent manner.

To the best of our knowledge, this is the first report that TCZ prospectively downregulates ROS levels in patients with RA. Furthermore, the antioxidative effect of TCZ may be more prominent that that of ETN.

The d-ROM value showed the highest correlation with MMP-3 (r = 0.637, p < 0.001), followed by CRP (r = 0.558, p < 0.001), ESR (r = 0.486, p < 0.01), and DAS28-4-ESR (r = 0.352, p < 0.05) [14] . In the current study, d-ROM value had a high correlation with DAS28, but no significant correlation was detected with MMP-3. The reason for this difference remains unknown. However, a significant correlation was detected in RA patients treated with TCZ, similar to that with ETN. Therefore, d-ROM values can be good surrogate markers of disease activity in RA.

Hirao et al. previously reported an average d-ROM value of 239.2 U.CARR in RA patients treated with TCZ, which was lower than the value in those treated with disease modifying antirheumatic drugs (464.2 U.CARR) and controls (osteoarthritis cases) (375.5 U.CARR). However, this evaluation was performed at only a single time point. In our study, patients were prospectively followed, and patients with comorbid diabetes mellitus, chronic kidney disease more than grade 3, and chronic obstructive pulmonary disease (COPD) were excluded, because these comorbidities permanently and endogenously upregulate oxidative stress markers. Therefore, our study may provide better evidence than previous reports [8] [9] .

There were some limitations in our study. First, only 11 cases were evaluated, and the small number reduces the statistical power. Second, comparison was not performed using other biologics such as TNF inhibitors. Third, the mechanism by which IL-6 inhibitory transactions downregulate ROS remains unknown.

Further examination of the pathways involved in signal transduction is important, and the key molecules involved in ROS downregulation by TCZ should be identified.

5. Conclusion

In summary, TCZ rapidly and significantly decreased ROS in patients with RA and d-ROM value in sera may be a useful marker of disease activity of RA.

Acknowledgements

We would like to thank Editage (www.editage.jp) for English language editing.